Rotary lamps in the prior art generally comprise a rotatable lamp cover to make the lamp have a better visual appearance and display effect and expand the scope of use thereof. However, conventional rotary lamps are structurally complicated. To allow for rotation of the lamp cover, the entire lamp including the lamp cover needs to be designed as a unitary closed type. The unitary closed type rotary lamp, having a complicated structure, is costly and does not facilitate replacement of a light source such as a bulb and a tube. Usually, it is preferable to have a professional repairer replace the light source. Furthermore, when a transmission mechanism is designed, the conventional rotary lamp integrates the transmission mechanism and a specific structure of a particular lamp in one piece, for example, one lamp can only be adaptable for one lamp cover so that adaptability and universality of the lamp are rendered undesirable.
Furthermore, conventional rotary devices not only need an individual motor but also require an output shaft of the motor and a rotational axis of the rotary object to be staggered from each other. As a result, the entire rotary device is structurally complicated and too large in size.